use vinegar and hot water.

1)put in half full vinegar to rad and shaking it.
2)drain out vinegar and put in hot water and shaking it.
3)repeat step 1 and 2 few time.
4)at last make sure there is no vinegar in ur rad, before u put in to loop ( u can repeat step 2 few time once ur rad is clean)

pls take note DONT put vinegar in rad more than 1 hr, cause it will eat copper.

correct me if i am wrong.

heheh sekali tengok i tot it was Austin Power's enlarger LOL!!